Experimental evaluation of ontogenetic diet transitions in summer flounder (<i>Paralichthys dentatus</i>), using stable isotopes as diet tracers

Abstract

We examined the rate of isotopic change of nitrogen (N) and carbon (C) and isotopic fractionation at two temperatures during several ontogenetic diet transitions in summer flounder (Paralichthys dentatus). We examined prefeeding larvae as they metabolize the maternal source of nutrition and evaluated three diet transitions in the early life stages of this species: (i) yolk dependency to first feeding on zooplankton, (ii) one zooplankton (rotifers) to another (Artemia), and (iii) zooplanktivory to piscivory. We used experimental results and simulations to contrast time- versus growth-based models for estimating parameters of isotopic change and fractionation. All rates of isotopic change were lowest for the transition between zooplanktivory and piscivory, most rapid for the transition from yolk dependency to first feeding, and generally lower at cooler temperatures. Estimates of fractionation were greater for N (2.8‰–3.8‰) than for C (0.23‰–0.91‰) but appeared to be unaffected by water temperature or fish life stage. Simulation results suggested that parameter estimates of isotopic change and fractionation may be compromised when growth rates are low unless sampling design is modified to address slow growth rates. We conclude that sampling strategy and the model used can influence the accuracy and precision of estimates of isotopic change and fractionation.